The present invention relates to an apparatus for rapidly mixing together exactly specified quantities of two or more fluids such as paints, enamels and dyes amongst others to form a homogenised fluid mixture.
In general, modem day paint manufacturing processes utilise a set of pigment pastes or concentrates which are mixed together with specified amounts of a white, black or green base paint to produce the desired colour and are diluted by adding specified amounts of solvent or varnish to obtain the required viscosity. In this way, a paint with specified physical properties such as colour, opacity, hue, saturation and viscosity can be obtained.
Typically, the time taken to produce a batch of paint is lengthy due to the lack of uniformity between different batches of concentrates and bases, and the subsequent need for an iterative process of testing and adjustment before the desired result is achieved. In most paint manufacturing processes such an iterative process was extremely time consuming, taking of the order of days for the required quantities of concentrates and bases to be determined. However, due to recent advances in paint production techniques, measurement of the physical properties of a paint mixture can be achieved in a matter of seconds, as described in PCT/BR96/00046. This has meant that analysis of the properties of a paint mixture is no longer the most time consuming step in the process of paint manufacture, and, in order to speed up the process still further, attention has needed to be focused on other steps in the process.
One of the steps in the paint manufacturing process that is relatively time consuming is the mixing of the various ingredients or components of the desired paint formula to be produced. This must be done so as to achieve a homogenous mixture of exact and repeatable quantities of the various ingredients in as little time as possible.
Mixing of the various components of a paint formula usually takes place in a mixing vessel such as a vat or barrel into which each of the components is poured and then mixed.
In order to enable mixing of the components, the mixing vessel must have a large enough volume to allow all the components of the formula to be added.
Addition of the components can be carried out using any one of three basic dosing systems:
(a) Gravimetric Dosing
In this system, the vessel is mounted on a weighing structure which is used to weigh the formula to which each component is dosed gravametrically in sequence.
(b) Volumetric Dosing
In this system, each component to be dosed has an individual dosing system which provides the correct dosage for each of the components to the mixing vessel. Normally, dosing pumps are used for this purpose, these having the inconvenience of requiring periodic calibration. The principal advantage of a volumetric dosing system over a gravimetric dosing system is the speed with which the components can be added to the vessel, since all the components can be added simultaneously. The volumetric dosing system is used to a great extent in commercial dosing machines.
(c) Simultaneous Dosing Controlled by Flow Rate Meters
This system brings together the individual advantages of each of the systems described above (precision and speed), because the dosing is controlled individually for each component using a mass flow rate meter. Coriolis effect mass flow rate meters provide the best solution for this type of dosing because they directly measure the variable mass and not volume, as do other meters. Measurement and control of the dosing using volumetric flow rate meters is affected by variations in density, temperature, etc.
In the dosing systems described in items (b) and (c) above, each of the various components of the paint formula to be dosed typically is injected into the vessel through an injection nozzle. This presents a problem with respect to the reliability of the dosing system, since it is difficult to control exactly the quantities of each of the components entering the mixing vessel, there being the possibility of spitting from the nozzles during injection as well as suck back of partially mixed paint ingredients, immediately after injection, and dripping from the nozzles during mixing.
After the components of the paint formula have been added to the mixing vessel, it is necessary to homogenise (mix) the components of the formula, and the time taken to mix the components may take from minutes to hours, depending directly on such factors as the volume of the vessel in which the components are mixed, the pumping capacity of the mixing impeller, as well as the individual differences in viscosity between the components of the formula. It should also be noted that during mixing or homogenisation of the various components of the paint formula the composition of the mixture may alter due to evaporation of the solvents used, since normally the mixing vessels are open.
Object of the Invention
The object of the present invention is to provide a fluid mixing device, and fluid injection valve for use therewith, for rapidly and continuously mixing together exactly specified quantities of two or more fluids, which overcome the above mentioned problems in the state of the art.
According to a first aspect of the present invention, a fluid mixing device, for the continuous mixing of two or more fluids, comprises:
a mixing chamber having fluid contact surface means defining an internal chamber region;
at least one fluid inlet means provided in the fluid contact surface means, for feeding at least one fluid into the chamber region;
at least one fluid outlet means provided in the fluid contact surface means, for feeding fluid out of the chamber region;
fluid mixing means within the chamber region, capable of inducing mixing of two or more fluids within a mixing region;
wherein the chamber region has a configuration which substantially corresponds to the configuration of the mixing region.
The mixing chamber comprises an outer fluid containment portion and an inner core, a first area of the fluid contact surface means being formed on the fluid containment portion and a second area of the fluid contact surface means being formed on the inner core.
For preference, the first area of the fluid contact surface means has a substantially spherical form, and at least one of the fluid inlet means is provided in this area.
Preferably, at least one of the fluid outlet means is also provided in the first area of fluid contact surface means, and at least one of the fluid inlet means is located below this outlet means.
For further preference, the mixing chamber is further provided with pressure control means, for controlling the pressure within the chamber region in relation to the pressure externally of the chamber.
According to a second aspect of the present invention, a valve means for use in the fluid mixing device according to the first aspect of the present invention, comprises:
a body portion having at least one fluid entrance aperture, for allowing fluid to flow into the body portion;
a fluid exit aperture, for allowing fluid to flow from the body portion;
entrance aperture sealing means having biasing means for biasing the entrance aperture sealing means into a sealing position in which the fluid entrance aperture is sealed; and
exit aperture sealing means having biasing means for biasing the exit aperture sealing means into a sealing position in which the fluid exit aperture is sealed;
wherein the entrance and exit aperture sealing means are adapted to allow passage of fluid respectively into and out of the body portion, according to a specified pressure differential between the pressure externally of the entrance aperture and the pressure externally of the exit aperture.